Evaluation of the ideal position of the maxillary incisor relative to upper lip thickness

Abstract

The anteroposterior position of the maxillary incisors has been studied since the beginning of cephalometric research. Most reports of ideal position have been based on measurements made on subjects with Class I occlusion without consideration of other facial variables. However, the ideal position is reflected in the soft tissues by the position of the lips. The purpose of this study was to consider the position of the maxillary incisor relative to other factors, including the thickness of the upper lip, and to evaluate its most aesthetic position using profile photographs. The subjects in this study were 130 patients with Class I occlusion; their sex, age, thickness of the upper lip, and angular position of the maxillary incisor were recorded. From these 130 patients, 70 profile photographs that met the inclusion criteria were chosen for further evaluation. A survey was conducted among 60 lay people, 60 dentists, and 60 orthodontists. They were asked to classify the sets of photographs, from the most esthetic position of the upper lip to the least esthetic. For patients with thin lips, raters tended to prefer a more protruded position of the incisor than normal or between 8.0mm and 11.5mm in front of the Na-B bone and 4mm in front of the Na-A bone. For patients with thick lips, the position of the incisor did not affect the perception of the profile. A correct skeletal scheme or Class I occlusion does not necessarily result in ideal facial harmony. Therefore, it will be necessary to consider all the factors that come into play, especially the lips, which are a key element in facial esthetics.